Promise One by One

tasks.js

(() => {
  var p1 = (val) => new Promise((resolve, reject) => {
  console.log('sent process 1')
  setTimeout((val) => {
    console.log('done1')
    resolve(val)
  }, 100, 'one');
  });
  var p2 = (val) => new Promise((resolve, reject) => {
    console.log('sent process 2')
    setTimeout((val) => {
      console.log('done2')
      resolve(val)
    }, 200, 'two');
  });
  var p3 = (val) => new Promise((resolve, reject) => {
    console.log('sent process 3')
    setTimeout((val) => {
      console.log('done3')
      resolve(val)
    }, 300, 'three');
  });
  var p4 = (val) => new Promise((resolve, reject) => {
    console.log('sent process 4')
    setTimeout((val) => {
      console.log('done4')
      resolve(val)
    }, 400, 'four');
  });
  // var p5 = (val) => new Promise((resolve, reject) => {
  //   console.log('sent process 5')
  //   reject('reject');
  // });
  [p1, p2, p3, p4].reduce((promise, task) => promise.then(async processRes => processRes.concat(await task())), Promise.resolve([])).then((allRes) => {
    console.log('done~~~~', allRes)
  })
  // Promise.all([p1, p2, p3, p4, p5]).then(values => {
  //   console.log(values);
  // }, reason => {
  //   console.log(reason)
  // });
})()